The isolated perfused kidney will be used as a tool to investigate metabolic and hormonal factors influencing the transport of water and electrolytes. The effects of insulin, glucagon and prostaglandins on renal tubular handling of sodium, potassium and chloride will be examined. The secretion of renin by the perfused kidney will be measured and effects on renin secretion of cellular swelling, perfusate tonicity, serum oncotic pressure, and in vivo inhibitors like propranolol and vasopressin will be evaluated. The metabolism of vitamin D derivatives by the perfused rat kidney will also be investigated. Active chloride transport in the teleost gill and the rectal gland of elasmobranchs will be the subject of further research. The relationship of metabolism to chloride transport will be examined, the oxygen cost of chloride secretion measured and its hormonal control investigated. Further experiments are planned dealing with the cotransport of chloride with sodium in membrane vesicles. The relationship of prostaglandin secretion to defects in urinary concentration will be evaluated in patients with various disorders of renal concentrating ability.